1. Field of the Invention
The present invention relates to an exposure apparatus, an exposure method, and a device manufacturing method. More particularly, the present invention relates to an exposure apparatus and an exposure method used to manufacture a semiconductor device and the like in a lithographic process, and a device manufacturing method using the exposure apparatus.
2. Description of the Related Art
Conventionally, in the lithographic process to manufacture a semiconductor device and the like, various exposure apparatus have been used. In recent years, exposure apparatus such as the reduction projection exposure apparatus based on the step-and-repeat method (the so-called stepper), and the scanning type projection exposure apparatus based on the step-and-scan method (the so-called scanning stepper), are becoming mainstream. The stepper reduces and transfers a mask pattern formed on a mask (also called a reticle), which is proportionally magnified 4 to 5 times, onto a substrate subject to exposure. And, the scanning stepper is an improvement of the stepper.
With these exposure apparatus, in order to cope with finer integrated circuits and achieve higher resolution, the exposure wavelength has shifted toward shorter wavelength. Recently, the exposure wavelength in practical use is 193 nm of the ArF excimer laser, however, exposure apparatus using shorter wavelength such as the F2 laser beam having a wavelength of 157 nm or the Ar2 laser beam having a wavelength of 126 nm are also being developed.
Light in the wavelength region called vacuum ultraviolet which wavelength belongs to the bandwidth of 200 nm to 120 nm such as the ArF excimer laser beam, the F2 laser beam, or the Ar2 laser beam, has low transmittance to optical glass. Therefore, the glass material that can be used is limited to fluoride crystal such as fluorite, magnesium fluoride, and lithium fluoride. In addition, vacuum ultraviolet light is greatly absorbed by gas such as oxygen, water vapor, and hydrocarbon gas (hereinafter referred to as xe2x80x9cadsorptive gasxe2x80x9d) existing on the optical path. It is also greatly absorbed by contaminants in the case organic contaminants or water and the like adhere on the surface of the optical elements. Therefore, gas existing on the optical path needs to be replaced with a low absorptive gas, that is, inert gas such as nitrogen or helium (hereinafter referred to as xe2x80x9clow absorptive gasxe2x80x9d). When the gas is replaced, impurities concentration of organic contaminants, water, absorptive gas, and the like in the optical path where the exposure light passes through is lowered so as not to exceed several ppm.
The design concept of the ArF excimer laser exposure apparatus and the F2 laser exposure apparatus is to exclude the absorptive gas as much as possible from the optical path from the light source to the wafer. Based on the concept, for example, there is an idea of covering the reticle stage and the wafer stage with casings as is with the optical elements making up the projection optical system, and structuring each casing as an independent room so that the gas in each room may be exchanged with a low absorptive gas with high purity, for example, such as helium.
In such a case, either idea had been employed; to supply low absorptive gas with high purity to each room, circulate the gas and then simply exhaust the gas outside (gas of which purity such as nitrogen has decreased due to the influence of impurities (such as absorptive gas or organic materials)), or to collect and store at least a part of the gas exhausted.
In addition, the idea was employed of supplying low absorptive gas with high purity to all the rooms in parallel.
With the method of exhausting outside the gas circulated in each room which purity has decreased or with the method of storing a part of the gas, as is described above, however, most of the gas was done away with without being recycled or just simply stored after being collected. Also, in the case of supplying low absorptive gas with high purity to a plurality of rooms respectively in parallel, a huge amount of gas is required.
For these reasons, the concept described above had to consume an enormous amount of expensive gas such as nitrogen gas, or helium gas, which is more costly. This increased the cost burden, and was likely to become the cause of increasing the production cost when manufacturing a semiconductor device.
Whereas, by simply reducing the amount of low absorptive gas consumed, that is, by reducing the amount of gas supplied into each room, the impurity concentration in the optical path will increase. And as a consequence, the transmittance of the exposure light will decrease, which becomes a cause of an exposure defect.
The present invention has been made in consideration of the circumstances described above, and has as its first object to provide an exposure apparatus and an exposure method capable of improving the usage of the low absorptive gas so that it is used effectively and wasteful consumption is suppressed, while maintaining the transmittance of the exposure light.
It is the second object of the present invention to provide a device manufacturing method that can improve the productivity when a device is manufactured.
According to the first aspect of this invention, there is provided an exposure apparatus that illuminates a mask with an energy beam from an energy beam source and transfers a pattern formed on the mask onto a substrate, the exposure apparatus comprising: at least one closed space which is located on an optical path of the energy beam between the energy beam source and the substrate; and a gas supply system which is connected to a first chamber being at least an arbitrary of the closed space and supplies a specific gas with a characteristic feature of having transmittance to the exposure beam to the first chamber, and supplies gas exhausted from the first chamber to the second chamber being at least an arbitrary of the closed space.
In this description, xe2x80x9cclosed spacexe2x80x9d includes the concept of closed space that is not completely in a sealed state in the strict sense of the word, other than space in a sealed state to the outside.
With this apparatus, the gas supply system supplies the specific gas which has a predetermined purity to the first chamber, and the gas exhausted from the first chamber is supplied to the second chamber. In this case, the specific gas which has circulated in the first chamber and the purity decreased to some extent due to degassing is supplied to the second chamber as the replacement gas. Therefore, for example, by supplying specific gas with high purity to the first chamber, and at least setting a chamber where the optical path of the energy beam is relatively short and is not seriously affected by the decrease in transmittance due to the absorption of the energy beam by impurities such as air in the optical path as the second chamber, the purity of the specific gas required in the first chamber and the second chamber can be sufficiently satisfied and the transmittance of the energy beam (exposure light) can be maintained. In addition, since the specific gas circulated in the first chamber is not exhausted outside and is used as the replacement gas of the second chamber, the usage efficiency of the specific gas can be improved, which leads to suppressing wasteful consumption of the specific gas (low absorptive gas).
In this case, the first chamber and the second chamber can be different chambers.
In this case, the exposure apparatus can further comprise: a movable optical member which is arranged between the energy beam source and the substrate; and a driving system which is connected to the optical member and drives the optical member, wherein a closed space formed in between a first optical element and a second optical element that are arranged in between the energy beam source and the substrate can structure the first chamber, and a closed space which houses at least a part of the optical member and the driving system can structure the second chamber. The first chamber, in this case, is formed in between the optical elements arranged along the optical path, so the main purpose of purging the interior with the specific gas is to remove the impurities as much as possible. Therefore, the purity level of the gas supplied to the first chamber needs to be high. On the other hand, the main purpose of purging the interior of the second chamber which houses the movable optical member and at least a part of the driving system with the specific gas is to exhaust the dust (particles) generated from the moving portion outside the chamber. So, the specific gas supplied to the second chamber may be a gas which purity is lower than the gas supplied to the first chamber. Accordingly, with the gas supply system supplying the specific gas to the first chamber, and also supplying the gas exhausted from the first chamber to the second chamber which houses the optical member and at least a part of the driving system, the purity of the specific gas required in each chamber can be sufficiently satisfied while maintaining the transmittance of the energy beam (exposure light) in the first and second chamber.
With the exposure apparatus in the present invention, the exposure apparatus can further comprise: an illumination optical system which is arranged in between the energy beam source and the mask and illuminates the mask with the energy beam from the energy beam source; and a projection optical system which is arranged in between the mask and the substrate and projects the energy beam via the mask on the substrate, wherein a housing which houses the illumination optical system, a mask chamber which houses a mask stage holding the mask, a barrel which houses the projection optical system, and a substrate chamber which houses a substrate stage holding the substrate can be arranged as the closed space, and at least one of the housings which house the illumination optical system and the projection optical system can structure the first chamber, and at least one of the mask chamber and the substrate chamber can structure the second chamber. In the case of replacing the gas within the illumination optical system housing, the barrel of the projection optical system, the mask chamber, and the substrate chamber respectively with the specific gas, the permissive concentration of impurities in the gas within the respective chambers, in other words, the purity level of the specific gas required in the respective chambers is not the same. That is, with the illumination optical system or the projection optical system where the optical path of the illumination light is long and many optical elements such as lenses are arranged, the interior needs to be filled with the specific gas which has an extremely high purity level to remove the impurities from the optical path. Meanwhile, with the mask chamber or the reticle chamber, the effect of impurities more or less existing on the optical path does not create a serious problem since the optical path is short. Accordingly, the gas supply system supplies the specific gas of a predetermined concentration to the first chamber, which is at least either the illumination optical system housing or the barrel of the projection optical system. And the specific gas that has circulated in the first chamber and the purity decreased to some extent due to degassing is supplied to the second chamber, which is at least either the mask chamber or the substrate chamber, as the replacement gas. Thus, the purity of the specific gas required in each chamber can be sufficiently satisfied while maintaining the transmittance of the energy beam (exposure light) in the first and second chamber.
With the exposure apparatus in the present invention, the gas supply system can further comprise a gas purity monitoring unit which monitors concentration of impurities in the gas exhausted from the first chamber and exhausts the gas outside when the concentration of the impurities exceeds a predetermined value. In such a case, the gas purity monitoring unit monitors the concentration of impurities in the gas exhausted from the first chamber, and if the concentration exceeds a predetermined value, then the gas is exhausted outside. Therefore, the purity of the gas supplied to the second chamber does not exceed a certain level.
In this case, the gas supply system can further comprise a gas purify unit that purifies the gas exhausted from the first chamber and improves purity of the specific gas in the gas exhausted. In such a case, the gas purify unit purifies the gas exhausted from the first chamber, and the purity of the specific gas in the exhausted gas is improved (can be restored close to the original purity). Also, in this case, due to the gas purity monitoring unit, the life of the gas purify unit can be extended.
In this case, the gas supply system can further comprise a gas supply route which separates the gas exhausted from the first chamber and partially supplies the gas to the gas purify unit and merges the gas having passed through the gas purify unit into remaining of the gas exhausted from the first chamber. In such a case, the gas supply route separates the gas exhausted from the first chamber, and a part of the gas is supplied to the gas purify unit. The gas which purity has increased by passing through the gas purify unit is merged with the remaining separated gas, and then the gas is supplied to the second chamber. Therefore, the purity of the specific gas supplied to the second chamber is not reduced more than necessary, and the life of the gas purify unit can be extended compared with the case when the gas exhausted from the first chamber is totally supplied to the gas purify unit.
In this case, the gas supply system can further comprise a temperature adjustment unit that has a chemical filter which removes impurities in the merged gas having passed through the gas supply route, and adjusts the gas to a predetermined temperature. In such a case, the gas which purity is increased by passing through the gas purify unit and then slightly decreased after merging with the remaining gas is supplied to the temperature adjustment unit. The impurities in the gas supplied are removed with the chemical filter, and the gas is then supplied to the second chamber after the temperature adjustment unit adjusts the temperature to a predetermined level. Accordingly, the gas supplied to the second chamber is gas which impurities are removed, the temperature adjusted, and the purity level relatively high. Therefore, the decrease in transmittance of the energy beam (exposure light) in the second chamber can be suppressed efficiently all the more.
With the exposure apparatus in the present invention, in the case the gas supply system comprises the gas purity monitoring unit and the gas purify unit, it does not necessary have to comprise the gas supply route described above. And, the gas supply system can further comprise a temperature adjustment unit that has a chemical filter which removes impurities in the gas having passed through the gas purify unit, and adjusts the gas to a predetermined temperature.
With the exposure apparatus in the present invention, the gas supply system does not have to comprise a gas purity monitoring unit, and can further comprise a gas purify unit which purifies and increases purity of the specific gas in the gas exhausted from the first chamber.
In this case, the gas supply system can further comprise a gas supply route which separates the gas exhausted from the first chamber and partially supplies the gas to the gas purify unit and merges the gas partially supplied to the gas purify unit into remaining of the gas exhausted from the first chamber.
In this case, the gas supply system can further comprise a temperature adjustment unit that has a chemical filter which removes impurities in the merged gas having passed through the gas supply route, and adjusts the gas to a predetermined temperature.
With the exposure apparatus in the present invention, in the case the apparatus does not comprise any of the gas purity monitoring unit, the gas purify unit, and the gas supply route, the gas supply system can further comprise a temperature adjustment unit that has a chemical filter which removes impurities in the gas exhausted from the first chamber, and adjusts the gas supplied to a predetermined temperature.
With the exposure apparatus in the present invention, it is preferable for the first chamber and the second chamber to be sealed chambers in a state sealed externally. In such a case, there is no need to worry about gas containing impurities concentrating from the outside. However, the first chamber and the second chamber do not necessarily have to be sealed chambers.
With the exposure apparatus in the present invention, the first chamber and the second chamber can be the same chamber.
With the exposure apparatus in the present invention, the gas supply system can be a gas circulation system which supplies the specific gas to the first chamber while maintaining purity of the specific gas within a predetermined range and replenishing shortage from exterior, collects the gas exhausted from the first chamber, and supplies the gas to the second chamber. In such a case, the gas circulation system supplies the specific gas to the first chamber located on the optical path of the energy beam between the energy beam source and the substrate, while maintaining the purity of the specific gas within a predetermined range and replenishing the shortage from the exterior. And the gas circulation system collects the gas exhausted from the first chamber and supplies it to the second chamber formed between the energy beam source and the substrate. In this case, the first chamber and the second chamber may be different chambers, or the first chamber and the second chamber may be the same chamber. Thus, most of the specific gas is re-used in the same or different closed space, and the usage efficiency of the specific gas (low absorptive gas) is improved and wasteful consumption suppressed. In addition, the gas circulation system maintains the purity of the specific gas supplied to the first chamber within a predetermined range. Therefore, the decrease in transmittance of the energy beam (exposure light) in the first chamber can be prevented.
In this case, of the first chamber and the second chamber, at least the first chamber may be the space existing in between the optical elements (such as lenses or mirrors) arranged on the optical path of the energy beam. Or, in the case the exposure apparatus further comprises: an illumination optical system which is arranged in between the energy beam source and the mask and illuminates the mask with the energy beam from the energy beam source; and a projection optical system which is arranged in between the mask and the substrate and projects the energy beam via the mask on the substrate, a housing which houses the illumination optical system, a mask chamber which houses a mask stage holding the mask, a barrel which houses the projection optical system, and a substrate chamber which houses a substrate stage holding the substrate can be arranged as the closed space, and the first chamber and the second chamber can be formed of one of the mask chamber, the substrate chamber, the housing which houses the illumination optical system, and the barrel which houses the projection optical system.
With the exposure apparatus in the present invention, the gas circulation system can comprise a gas circulation unit which supplies the specific gas to the first chamber, while replenishing shortage from the exterior and maintaining purity of the specific gas in accordance with an amount of returned gas exhausted from the second chamber.
With the exposure apparatus in the present invention, the gas circulation system can exhaust outside the gas exhausted from the first chamber without collecting the gas until concentration of impurities falls under a predetermined level, when initial gas replacement operation is performed to replace gas within the first chamber to the specific gas. In such a case, when the gas circulation system performs initial gas replacement operation to replace the gas inside the first chamber (gas containing much absorptive gas such as oxygen) to the specific gas, the gas is exhausted outside without being collected until the impurities in the gas exhausted from the first chamber falls below a predetermined concentration. So when the concentration of impurities (such as absorptive gas) is high in the gas exhausted from the first chamber, the gas circulation system exhausts the gas outside. Thus, the decrease in transmittance of the energy beam (exposure light) in the second chamber can be suppressed without the purity of the specific gas supplied to the second chamber deteriorating to the extreme.
In this case, the gas circulation system can include a judgement unit which judges that the concentration of impurities in the gas has fallen under a predetermined level by an elapse of a predetermined period of time after starting the initial gas replacement operation, when the initial gas replacement operation is performed. Or, the gas circulation system can include a judgement unit which has a concentration detection unit to detect concentration of at least one of impurities and specific gas in the gas and judges that the concentration of impurities in the gas has fallen under a predetermined level based on an output of the concentration detection unit when the initial gas replacement operation is performed.
With the exposure apparatus in the present invention, the gas circulation system can further comprise a gas purity monitoring unit which monitors concentration of impurities in the gas exhausted from the first chamber and exhausts the gas outside when the concentration of the impurities exceeds a predetermined value. In such a case, the gas purity monitoring unit monitors the concentration of impurities in the gas exhausted from the first chamber, and when the concentration of impurities exceeds a predetermined value the gas is exhausted outside. On the other hand, when the concentration of impurities is under the predetermined value, the gas is re-supplied to the second chamber. Accordingly, when the concentration of impurities of the gas exhausted from the fist chamber is low, the gas is re-used as the replacement gas of the second chamber. Thus, the usage efficiency of the specific gas (low absorptive gas) can be improved which leads to suppressing wasteful consumption of the gas. Meanwhile, in the case the concentration of impurities of the gas exhausted from the fist chamber is high, the gas is exhausted outside, so the decrease in transmittance of the energy beam (exposure light) in the second chamber can be suppressed without the purity of the specific gas supplied to the second chamber unnecessarily decreasing.
In this case, the gas circulation system can further comprise a gas purify unit that purifies the gas collected from the first chamber and improves purity of the specific gas in the gas collected. In such a case, the gas exhausted from the first chamber is collected and purified by the gas purify unit, and the purity of the specific gas in the exhausted gas can be improved (can be restored close to the original purity).
In this case, the gas circulation system can further comprise a temperature adjustment unit that has a chemical filter which removes impurities in the gas having passed through the gas purify unit and adjusts the gas to a predetermined temperature. Or, the gas circulation system can further comprise a gas supply route which separates the gas collected from the first chamber and partially supplies the gas to the gas purify unit and merges the gas partially supplied to the gas purify unit into remaining of the gas collected from the first chamber. In such a case, the gas supply route separates the gas collected from the first chamber, and partially supplies the gas to the gas purify unit. The gas which passes through the gas purify unit is purified so that the purity is increased, and then the gas is merged with the remaining gas and finally supplied to the second chamber. This arrangement can extend the life of the gas purity unit without the purity of the specific gas supplied to the second chamber unnecessarily decreasing, compared with the case when the gas is totally supplied to the gas purity unit.
In this case, the gas circulation system can further comprise a temperature adjustment unit that has a chemical filter which removes impurities in the merged gas having passed through the gas supply route, and adjusts the gas to a predetermined temperature. In such a case, gas which purity has slightly decreased because of merging with the remaining gas after passing through the gas purify unit is supplied to the temperature adjustment unit, where the impurities in the gas supplied is removed by the chemical filter and the gas adjusted to a predetermined temperature. Then the gas is supplied to the second chamber. Accordingly, the specific gas supplied to the second chamber is gas with relatively high purity, with the impurities removed and temperature adjusted.
With the exposure apparatus in the present invention, the gas circulation system can further comprise a gas purify unit that purifies the gas collected from the first chamber and improves purity of the specific gas in the gas collected, without comprising the gas purity monitoring unit.
In this case, the gas circulation system can further comprise a gas supply route which separates the gas collected from the first chamber and partially supplies the gas to the gas purify unit and merges the gas partially supplied to the gas purify unit into remaining of the gas collected from the first chamber.
In this case, the gas circulation system can further comprise a temperature adjustment unit that has a chemical filter which removes impurities in the merged gas having passed through the gas supply route, and adjusts the gas to a predetermined temperature.
With the exposure apparatus in the present invention, the gas circulation system can further comprise a temperature adjustment unit that has a chemical filter which removes impurities in the gas collected from the first chamber, and adjusts the gas supplied to a predetermined temperature, even if the exposure apparatus does not comprise the gas purity monitoring unit, the gas purify unit, or the gas supply route.
With the exposure apparatus in the present invention, in the case the gas supply system is the gas circulation system, the first chamber and the second chamber can be sealed chambers in a state sealed externally.
In addition, in the lithographic process, by performing exposure using the exposure apparatus in the present invention, the transmittance of the energy beam can be maintained so that exposure control with high precision can be maintained for a long period of time, as well as decrease the usage amount of the specific gas (low absorptive gas). Accordingly, the running cost can be reduced without decreasing the yield of the device, and as a consequence, the productivity of the device can be improved. Therefore, from the second aspect of the present invention, a device manufacturing method using the exposure apparatus in the present invention is provided.
According to the third aspect of this invention, there is provided an exposure method to illuminate a mask with an energy beam from an energy beam source and transfer a pattern formed on the mask onto a substrate, the exposure method comprising: supplying a specific gas with a characteristic feature of having transmittance to the exposure beam to a first chamber being at least an arbitrary of at least one closed space arranged on an optical path of the energy beam in between the energy beam source and the substrate, exhausting internal gas from the first chamber, and supplying gas exhausted from the first chamber to the second chamber being at least an arbitrary of the closed space.
With this method, the specific gas with a predetermined purity is supplied to the first chamber, and the gas exhausted from the first chamber is collected and supplied to the second chamber. In this case, the specific gas that has circulated the first chamber and the purity slightly decreased due to degassing and the like is collected and supplied to the second chamber as the replacement gas. Therefore, by supplying the specific gas with high purity to the first chamber, and arranging a chamber where the optical path of the energy beam is relatively short and the effects of the energy beam transmittance decreasing due to absorption by impurities such as air in the optical path do not cause a serious problem as at least the second chamber, the transmittance of the energy beam (exposure light) can be maintained while sufficiently satisfying the purity of the specific gas required in the first chamber and the second chamber. In addition, the gas which circulates the first chamber is used as the replacement gas of the second chamber without being exhausted outside, thus, the usage efficiency of the specific gas can be improved, which leads to suppressing wasteful consumption of the specific gas (low absorptive gas).
In this case, the first chamber and the second chamber can be different chambers.
In this case, the first chamber can be a closed space formed in between a first optical element and a second optical element arranged in between the energy beam source and the substrate, and the second chamber can be a closed space which houses at least a part of a movable optical member arranged between the energy beam source and the substrate and a driving system which drives the optical member.
With the exposure method in the present invention, when the first chamber and the second chamber are different chambers, the first chamber can be a housing which houses at least one of an illumination optical system which illuminates the mask with the energy beam from the energy beam source and a projection optical system which projects the energy beam via the mask onto the substrate, and the second chamber can be at least one of a mask chamber which houses a mask stage holding the mask and a substrate chamber which houses a substrate stage holding the substrate.
With the exposure method in the present invention, impurities concentration of the gas exhausted from the first chamber can be monitored, and the gas exhausted from the first chamber can be exhausted outside when the impurities concentration exceeds a predetermined value.
With the exposure method in the present invention, the gas exhausted from the first chamber can be purified and purity of the specific gas in the gas exhausted from the first chamber increased.
With the exposure method in the present invention, the specific gas can be supplied to the first chamber while maintaining purity of the specific gas within a predetermined range and replenishing shortage externally, and the gas exhausted from the first chamber can be collected and supplied to the second chamber.